Conventionally, PLCs (programmable logic controllers) for controlling industrial machines and the like installed on production lines in factories have been known.
A PLC includes a CPU unit for controlling the PLC, an input unit to which a signal from a sensor is input, and an output unit outputting a control signal to an industrial machine or the like. The CPU unit has a memory storing a user program. This user program is configured to be editable by a tool apparatus connected to the CPU unit.
In the PLC, a process of capturing a signal input to the input unit into the memory of the CPU unit, a process of executing the user program, a process of writing the result of execution of the user program (calculation result) to the memory and sending the calculation result to the output unit, and peripheral processes such as exchanging data with the tool apparatus are performed repeatedly. The PLC thus controls the industrial machine or the like based on an input from the sensor.
Moreover, conventionally, PACs (programmable automation controllers) having the advanced software functionality of personal computers and the reliability of PLCs also have been known (see Patent Document 1 (JP 2009-181443A), for example).
A PAC disclosed in Patent Document 1 (JP 2009-181443A) is configured to execute a plurality of tasks concurrently by time sharing and to execute each task with a period corresponding to that task. That is to say, in this PAC, processing is performed in a multitasking manner. It should be noted that each task contains execution of a user program corresponding to that task.
Patent Documents    Patent Document 1: JP 2009-181443A